This invention relates to a coordinate input apparatus for calculating a position, which has been designated by a vibrating input pen, based upon vibration that has been input to a vibration transfer plate by the vibrating input pen. The invention relates further to a method of controlling this coordinate input apparatus and to a computer-readable memory for such control.
Tablets for inputting coordinates by a stylus pen (input pen) and digitizers have become widely available as coordinate input devices. Coordinate input by means of an input pen serves as an excellent human interface that approximates the pen-and-paper manner of input with which the user is well accustomed.
The input pen used with such a tablet or digitizer has a pen pressure sensing function in order to better mimic a writing instrument. More specifically, a pressure sensing mechanism is provided inside the input pen and information indicative of the pen pressure sensed is output to a host computer along with coordinate information indicating the position input by the pen. On the basis of the coordinate information and pen pressure information, the host computer alters the writing thickness or density of an entered line to provide a sensation nearer to that of existing writing instruments.
By way of example, a coordinate input apparatus disclosed in the specification of Japanese Patent Publication (KOKOKU) No. 5-62771 utilizing ultra sonic wave to sense input coordinates calculates the position of input coordinates by sensing a delay in the time of waves that propagate along a tablet, which is the input surface. Since the tablet used in this coordinate input apparatus does not employ any highly intricate means such as matrix wiring, the apparatus can be provided at low cost. Moreover, if transparent plate glass is used as the tablet, a coordinate input apparatus having a higher degree of transparency than other such apparatus using different techniques can be constructed. Further, as set forth in the specification of Japanese Patent Publication (KOKOKU) No. 6-48456, there is known an arrangement in which the sensing precision of the apparatus is improved by calculating pen pressure based upon the magnitude of propagating vibration (the amplitude of the signal sensed).
In the conventional coordinate input apparatus, however, the sensing effectiveness of the apparatus is judged upon calculating pen pressure based upon the sum of signal amplitudes sensed by sensors. In order to utilize this pen pressure information as the actual pen pressure information indicative of the input pen, therefore, more detailed pen pressure information is required. In other words, if pen pressure information is obtained as the sum of the amplitudes of sensed signals, the amount of change in pen pressure signal level differs depending upon the location at which the input is made (in a case where distances from the sensors differ) and, hence, accurate pen pressure cannot be calculated.